The present invention concerns a microstructure including a circuit integrated in a substrate on one upper or lower surface of which is arranged a flat coil, in particular a spiral coil galvanically deposited on a passivation layer provided on the surface of the substrate. More particularly, the invention concerns a microstructure including an electronic circuit formed by a plurality of transistors integrated in a semiconductor substrate and a flat coil arranged at the surface of the semiconductor substrate.
Within the scope of the present invention, in order to reduce to the maximum the dimensions of the developed microstructure, said flat coil is superposed at least partially with said aforementioned electronic circuit. However, within the scope of the development of this microstructure of reduced dimensions, the inventor has observed that the magnetic field generated by the flat coil-has an influence on certain sensitive transistors of the integrated electronic circuit under the surface defined by the flat coil. In particular, the sensitive transistors are those which operate with a relatively low current.
In order to overcome this problem detected within the scope of the present invention, the invention concerns a microstructure including an electronic circuit formed by a plurality of transistors integrated in a semiconductor substrate and a flat coil formed by a conductive wire or a conductive path extending in a spiral, this coil being arranged on an upper or lower face of the semiconductor substrate, each of said transistors being formed by at least two regions defining respectively a source and a collector between which an electric current is generated as a function of the electric state of the transistor, this microstructure being characterised in that at least a few transistors of said plurality of transistors and the surface defined by said flat coil are superposed with each other, at least the set of transistors, having high sensitivity when operating with a relatively low current among these few transistors being arranged so that said source and said collector of each of them are aligned along a direction perpendicular to the portion of said conductive wire or said conductive path situated in proximity to the transistor.
As a result of these features, the magnetic field generated by the flat coil is parallel to the alignment of the source and the collector of each of the transistors of the set of transistors having high sensitivity. Thus, the electrons forming the electric currents flowing in these transistors between the sources and collectors thereof are not subjected to Lorentz force and, in the case of field effect transistors (FET), the depth of the channel between the source and the collector is not affected by the presence of the coil superposed with the electronic circuit integrated in the substrate acting as a support structure for said coil.